Yeast glycan and process of making same

ABSTRACT

This application covers a yeast product which is derived from ruptured yeast cell walls and is known as yeast gum or yeast glycan. The yeast glycan is separated from the soluble parts of the yeast, purified, and dried. The yeast glycan increases the viscosity of aqueous fluids when rehydrated. The suspensions of yeast glycan also have a bland flavor, a &#39;&#39;&#39;&#39;fat-like&#39;&#39;&#39;&#39; mouth feel, and a sheen in appearance. Yeast glycan can be substituted for fat in certain dietary type food products, such as salad dressing, ice cream, etc.

United States'Patent n91 Sucher et a1.

[451 Feb. 18,1975

1 1 YEAST GLYCAN AND PROCESS OF MAKING SAME [22] Filed: Nov. 29, 1972 [21] Appl. No.: 310,452

[52] U.S. Cl 426/60, 426/148, 426/204,

426/212, 426/213, 426/364, 426/380, 426/431 [51] Int. Cl. A23j l/18, A231 H28 [58] Field of Search 426/60, 148, 364, 204,

[56] References Cited UNITED STATES PATENTS 3,268,412 8/1966 Champagnat et a1 195/3 3,585,179 6/1971 Samejima et a1. 260/112 3,615,654 10/1971 Ayukawa et al. 99/9 3,634,194 1/1972 Frankenfeld et a1.... 195/28 3,681,195 8/1972 Suekane et a1, 195/4 3,718,541 2/1973 Kalina 195/28 3,725,075 4/1973 Muroi et a1. 99/14 Primary Examiner-James R. Hoffman Attorney, Agent, or FirmGravely, Lieder & Woodruff [57] ABSTRACT This application covers a yeast product which is derived from ruptured yeast cell walls and is known as yeast gum or yeast glycan. The yeast glycan is separated from the soluble parts of the yeast, purified, and dried. The yeast glycan increases the viscosity of aqueous fluids when rehydrated. The suspensions of yeast glycan also have a bland flavor, a fat-like" mouth feel, and a sheen in appearance. Yeast glycan can be substituted for fat in certain dietary type food products, such as salad dressing, ice cream, etc.

16 Claims, 1 Drawing Figure YEAST GLYCAN AND PROCESS OF MAKING SAME BACKGROUND OF THE INVENTION Yeasts, throughout history, have been used to leaven bread and to brew ale, beer and wines. In the l930s, residual yeast from brewing operations and yeast produced as bakers yeast were dried and used for food purposes as a source of vitamins, minerals and protein. Dried food yeast contains approximately 33% to 40% true protein. In food usages, dried yeasts have been used at low levels in bread, cereals, peanut butter mixtures, other food products, and vitamin supplements as a source of protein, vitamins, minerals, and unknown nutrients. The levels of dried yeasts used in food products has never generally exceeded more than 5% because dried food yeasts have no functional values for food processing, and, at higher levels, contribute a distinct taste to the food product.

Yeast fractions have been used as a source of nutrients and are made from yeasts which have been autolyzed or whose cells have been broken up by mechanical means. In these cases, the protein has been recovered from the broken up yeast cells by alkaline extraction or solubilized by autolysis by the yeast enzymes themselves. These solubilized nutrients are then recovered by various methods. These commercial processes for recovering yeast protein and for producing yeast extracts all discard the extracted and washed yeast cell debris as a waste product.

We have discovered that the processing of food yeast to remove the major portion of the protein (as set forth in our copending application entitled YEAST PRO- TEIN ISOLATE WITH REDUCED NUCLEIC ACID CONTENT AND PROCESS OF MAKING SAME Ser. No. 310,469, filed Nov. 29, 1972) yields an insoluble residue consisting ofa mixture of whole yeast cell walls, fragments of yeast cell walls, and some proteinaceous materials. This residue, when recovered by drying, yields a bland yeast product which has unique functional characteristics.

One of the primary functional characteristics of this yeast fraction is its ability to hold water and give thickening properties in aqueous food systems.

The cell wall debris is water washed to a relatively constant protein content and is composed of cell wall fragments and what appears to be whole cells containing a methylene blue stainable material. We call this mixture, which consists of cell walls and whole cells with methylene blue stainable material, yeast gum or yeast glycan. The whole cells with stainable material are in the smaller amount. It is not known whether these whole cells have the same cell composition as unprocessed yeast cells. The cells apparently have approximately the same crude protein content as the unprocessed cell.

We have further discovered that the addition of this yeast glycan to liquid food systems, in the proper proportions, gives the food product a fat-like" mouthfeel even when these food products contain little or no fat. This is very useful in formulating low-calorie products, such as salad dressing, ice cream, puddings, sour cream based dips. etc.

We also have discovered that satisfactory yeast glycan preparations can be derived from not only the bakers yeast strains, such as Saccharomyces cerevisiae; but also from brewers yeast strains, such as Saccharomyces carlsbergensis; a lactose utilizing food yeast, Sacharomyces fragilis; and strains of Candida such as C. utilis. Saccharomycesfragilis has recently been reclassifled to Kluyueromyces fragilis. It has further been discovered that the yeast glycans can be derived from these various strains of yeast which have been grown on a variety of media. The glycans from different strains vary in some degree in their composition, but all have the ability to increase the viscosity of water whenisolated by the process described in the invention.

It is known from the literature that yeast cell walls contain a yeast glucan with glucose linkages with a l-6 main chain and l-3 side chain. Yeast mannans having a structure consisting of a backbone of l-6 mannopyranose units with 1-2 and l-3 link side chains attached through the No. 2 carbon of the backbone also have been isolated from the cell walls. This yeast mannan has been isolated by autoclaving at pH 7 or heating in strong alkali to give the soluble mannan which is isolated as a copper complex. Chitin is another fraction isolated from yeast cell walls and it has l-4 glucose linkages linked to N-acetylglucoseamine located near bud scars. The crude protein content of bakers yeast cell walls cited in the literature depends upon the method of preparation and usually falls between 5 and 20%.

Our product probably contains some or all of the foregoing constituents in addition to the unrefined portions previously discussed. All of these fractions in combinations give the unique properties and functions of our glycan.

We have discovered that when ruptured yeast cells are extracted with alkali, such as sodium hydroxide, and the residual cell debris washed thoroughly with water, a yeast food product is produced which can be dried by freeze drying, spray drying, drum drying or other methods of dehydration. This yeast fraction has a high level of carbohydrates, a low level of protein, a low but significant amount of lipid, and a low level of nucleic acid. It has been discovered that this yeast fraction can be incorporated in a variety of processed food products in place of lipid material and the food product will retain the excellent eating quality of a high-fat food product without the attendant calories of a high fat product.

I The nucleic acid of yeast is mainly ribonucleic acid or RNA, and in this application these terms are used interchangeably.

DESCRIPTION OF DRAWING The drawing is a schematic flow sheet of the process of this invention.

DETAILED DESCRIPTION Our process is comprised of the following steps: production of yeast cells, rupture of the cells, separation of the insoluble cell wall fragments from the soluble cytoplasmic fraction, purification and conditioning of the glycan, vacuum concentration, and drying.

Yeast cells (biomass) is produced by methods known to those versed in the art. We preferably use biomass of strains of Saccharomyces and Candida grown on food grade nutrients in batch and continuous fermentation. However, the main considerations are that the yeast be of food grade and produced in good yield.

The biomass is harvested by centrifugation or filtration, and water washed. When necessary, dilute alkali may be incorporated in the wash to remove adhering color and taste bodies. The yeast cells are ruptured by any of several known methods, such as, high pressure homogenization, attrition in a sand or colloid mill, sonic disintegration, repeated freeze-thaw cycles, lytic enzymes, and the like. The main consideration is to rupture the majority of cells under such conditions that the majority of the non-glycan materials remain in the soluble state to facilitate from the glycan. The ruptured cell system (homogenate) may be diluted, warmed and pH adjusted to favor processability.

The homogenate is separated by centrifugation and- /or filtration into a cell wall residue and an extract usually referred to as the alkali extract. A protein isolate and a meat flavored extract can be recovered from the alkali extract. The cell wall residue is processed to the yeast glycan.

Cell rupture, extraction of solubles, and processability are affected by pH, temperature, time, solids concentration, and homogenizer efficiency. Our usual method of measuring the extent of cell rupture is to determine the amount of nitrogen that remains soluble as follows:

7(- N Extractability l X (g N in supernate after centrifugation/g N homogenate before centrifugation) The yeast biomass after washing has a pH 4.5-6.5. The biomass is usually chilled, then passed through a Manton-Gaulin homogenizer to a chilled receiver. The process is repeated for a total of three passes. At least three passes are needed to obtain maximum cell rupture. ln practice, the biomass was homogenized at the ambient pH of the yeast, namely 4.5-6.5. Cell rupture can also be achieved at higher pHs up to at least pH 9.5, but the subsequent separation of the cell wall residue from the solubles becomes more difficult.

The effects of pH, solids concentrations, and homogenizer efficiency upon the N extractability of Candida urilis and on Saccharomyces cerevisiae are shown in Table I and Table ll.

The data ofTables l and ll show that extraction of the soluble nitrogenous materials can be carried out at least over the pH range of about 5.5 to about 11. Process considerations further limit the extraction pH to the range of about 7 to about 10, with pH 9.5 considered the optimal balance between extraction and subsequent separation of the cell wall residue from the solubles. Extraction is best at a low solids content, but again a consideration of process rates led to the adoption of a solids content of about 2.5 to about 4%. Extraction time can be varied between about 5 and about 60 minutes at extraction temperature of about 0C. to about 60C. preferably 25-60C. The best process rate of the subsequent separation of the cell wall residue from the solubles are obtained when the extraction is done at 60C. for 5 to 20 minutes, at pH 9.5. With Candia'a utilis and Saccaramyces cerevisiae, each pass from I to 5 through the homogenizer improves the nitrogen extractability presumably by rupturing more cells. A three pass system has been adopted as a good balance between efficiency of processing and cost. The pressure is between 5,000 and 15,000 PSIG. The temperature is between 0 and 60C. The pH is 4.5 to 6.5.

Taking N extractability and processing requirements into consideration, the optimal process to obtain the insoluble cell wall material is (1) growing a food grade yeast on a nutrient media, (2) harvesting and washing TABLE I Effect of Extraction pH, Solids Level, and-Ho'mogenizer Efficiency Upon Nitrogen Extractability of Candida utili:

Chilled suspensions of Candida uIiIis at pH 5.0-5.5. 740% solids were homogenized by means of Manton-Gaulin homogenizer. The chilled homogenate was recycled through the homogenizer repeatedly to give one, two, three or four pass homogenate. The homogenate was diluted with up to 2.0 parts of water. and adjusted in pH. The diluted homogenates were incubated for 30 min. at 50C. and then centrifuged. The nitrogen contents of the diluted homogenate, and of the supernate were measured by the Kjeldahl method. 7: N extractions were calculated.

No. of Passes Solids Content 7: Nitrogen pH of Extracted Extraction Good Medium or Poor separation of cell wall residue and solubles.

TABLE ll Effect of Extraction pH. Temperature, Time, Solids Content, and Homogenizer Efficiency Upon the Nitrogen Extractability of Saccltarumyces ceret'isiae Chilled suspensions of commercial baker's yeast at ambient 'pH of 6-6.5. 7-l07l solids, were homogenized by means of a Manton-Gaulin homogenizer. The chilled homogenate was recycled through the homogenizer to give one, two or three passes. The homogenates were diluted with up to two volumes of water and adjusted in pH. The diluted homogenates were incubated for 5-60 minutes at 25-60C. and centrifuged. The nitrogen contents of the homogenates and supernates after centrifugation were measured by the Kjeldahl method. 1' N extractions were calculated.

7: Solids Time C. Number of 7c Nitrogen pH Content (min) Passes Extractability emp.

9.5 9.] 30 25 3 83 9.5 4.8 30 25 3 84 9.5 3.l 30 25 3 92 9.5 3.l 30 25 2 9.5 3.l 30 25 l 63 9.5 3-4 5 5O 3 9i 9.5 3-4 20 5O 3 93 9.5 3-4 30 5O 3 96 9.5 3-4 60 50 3 96 9.5 3-4 5 60 3 93 9.5 3-4 20 60 3 94 9.5 3-4 30 60 3 9! 9.5 3-4 60 60 3 4.0 3-4 30 25 3 33 5.0 3-4 30 25 3 36 6.0 3-4 30 25 3 79 7.0 3-4 30 2S 3 93 TABLE II-Continued Effect of Extraction pH, Temperature. Time, Solids Content, and Homogenizer Efficiency Upon the Nitrogen Extractability of Sarclrarumyces cerevisiae Chilled suspensions of commercial bakers yeast at ambient pH of 6-6.5, 740% solids, were homogenized by means of a Manton-Gaulin homogenizer. The chilled homogenate was recycled through the homogenizer to give one, two or three passes. The homogenates were diluted with up to two volumes of water and adjusted in pH. The diluted homogenates were incubated for 5-60 minutes at 25-60C. and centrifuged. The nitrogen contents of the homogenates and supernates after centrifugation were measured by the Kjeldahl method. 7: N extractions were calculated.

7: Solids Time C. Number of 7r Nitrogen pH Content min.) Passes Extractability emp.

The cell wall residue is purified by water washes, or by homogenization and water washes followed by centrifugation to separate the unruptured cells. The glycan is usually concentrated in vacuo to provide economy of drying to a powder by spray drying, drum drying and the like. An added benefit of the in vacuo concentration is the removal of trace yeastly flavor to provide a bland product. The in vacuco concentration is important where the cell wall residue is not homogenized prior to washing. The conditions of in vacuo drying are as follows: Time to 60 min.; Temp. 120F. to 200F., Vacuum: to 28 inches Hg; Concentration Factor: 5% to 20% solids.

The final yeast glycan product has a composition of about 5-20% crude protein, about 0.1-3% lipid, about l-3% nucleic acid, about 0.5-3% ash, and from about 60-95% carbohydrate. The yeast glycan produces a visirregularly shaped fragmented cells and cell walls (from about 70 to about 100%) with a lesser amount (from about 0 to about 30%) of whole cells containing methylene blue stainable material.

Physical characteristics of our yeast glycan product were determined when suspensions of 5% yeast glycan (lot 091146) in water were inspected microscopically and photographed.

Photomicrographs were prepared under the following conditions: Heine Phase contrast, dark field setting, 40 X phase objective, green filter,.light at 6 A, l/2 second exposure, magnification 500 X x, Polaroid type lO7.

Examination of the mounts and of the photomicrographs reveal that: yeast glycan is composd almost entirely of pieces of cell walls of irregular shape and form. Some unfractured cells are visible, and these unfractured cells appear similar to bakers yeast cells. Empty cells, that is, cells whose outer boundaries are visible and unbroken but which appear devoid of cytoplasma within the cell outline are not present.

In the following Table, Table III, yeast biomass was prepared in fermentations by processes known to those versed in the art. The yeast biomass was harvested by centrifugation and washed twice with water. The yeast cells were ruptured by means of a Manton-Gaulin high pressure homogenzier. The ruptured cells and cell wall fragments were harvested by differential centrifugation and constitute the unrefined yeast glycan. The unrefined yeast glycan contains cytoplasmic constituents that can be removed by washing. The progress of the purification of the yeast glycan is followed by measuring the protein content. The effect on the protein content and on product yield of subjecting the unrefined yeast glycan to repeated washingis shown in Table III. An alternative method of purification is to rehomogenize the cell wall debris prior to washing. This method will be described in more detail hereinafter.

TABLE III Purification of Yeast Glycan by Repeated Water Washing Source of Yeast Glycan Yield (2) in No. of Washes Protein Content of Yeast Glycan (l) in grams on dsh. No. of Washes .S'ar'cluirumyres u'revisiae Sacr'ltummyces (arlsher ensis Sarc/iarmnyves frugilis Candida ulilis Y-QOO Candida utilis Y-l084 Kjeldahl N X 6.25 (dry solids basis) Yield I00 X g solids recovered as yeast glycan/g initial yeast solids Crown in batch fermentation using molasses as a carbon source.

' Brewers yeast recovered after fermentation of wort.

Grown in batch fermentation using milk whey as a carbon source.

cosity of at least about 500 centipoises when suspended in a 10% aqueous solution by weight at a temperature of 25C. The yeast glycan produced from homogenized yeast has an average fragment size of about 3.8:: 0.8 by about 2.4: 0.7 microns. It is composed principally of The washed yeast glycan can be recovered after washing by various methods of drying such as spray drying, drum drying or lyophilization. The composition of the lyophilized yeast glycans obtained after 4-5 water washes is shown in Table IV.

TABLE IV Composition of Washed Yeast Glycan monosaccharides formed on acid hydrolysis.

TABLE IV Continued Composition of Washed Yeast Glycan ""14 Protein 6.25 (/1 Kjeldahl N /1 Nucleic Acid N).

Nucleic Acid determination: About 50 mg. sample is digested with 5 ml. o1'0.2 N KOH for 30 minutes at 100C. The digest is acidified with 5 ml. HCll) Citrate reagent (0.4 M citrate buffer. pH 2.2 containing 1.7 ml.. 70% HC per 100 ml.). The residue is removed by centrifugation. The A of the suitably diluted supernatant is measured. The ex \inction coeflicient of 31.7 A ml/mg. is used to Calculate RNA. The RNA content is corrected for the A contribution of protein fragments in the hydrolysate as measured by the Lowry method.

The ration of glucose to mannose (G/m) of the glycan was established by quantitative determination of the syliatcd The yeast glycans rehydrate to viscous suspensions composition per liter; rehydrated dry cheddar cheese which have suspension freeze-thaw stability, and are whey which had been heated and filtered to clarity,

capable of conferring a full-fat mouth feel despite the equivalent to 150 g. lactose; ammonium sulfate, 36.2 absence of fat in the yeast glycan and in the food forg.; 85% phosphoric acid, 24.5 ml. The volume was mulation. The ability to form viscous suspensions is made to 1 liter with potable water. This liquid feed shown in Table V. stock was supplied completely and continuously during TABLE V Viscosity of Yeast Preparations The viscosity of a 10% suspension of lyophilized yeast glycans was measured at pH 7, C. using a Brookfield LVT, Helipath Stand. Spindle TE at 12 rpm.

Source of Yeast Gum Centipoise After Rehydrating at pH 7. 25C.

'Refrigeratcd overnight. then warmed to 25C.

The laboratory preparation of yeast glycan from the 1 1 hours at an increasing rate of 1.14. The'yeast growth yeast strain, Saccharomyces fragilis is presented in Exbroth was maintained at pH 5.7 by use of alkali. The ample No. l. yeast growth broth temperature was 30C. Aeration by sparger and impellor was at a rate of 3 volumes air per EXAMPLE NO. 1 volume of growth broth per minute.

. Sta e 1 reduced yeast dry substance equivalent to Preparat'on of Yeast 9? from sacchammyces 32% if th: lactose supplied. This Stage 1 yeast confmglhs tained 7.7% and 1.5% 'P. 7

Preparation of Biomass: i Stage 2 was stocked with 16.4 g. dry substance equiv- A primary growth stage was prepared as follo s! Dry alent of Stage 1 yeast. The stock yeast was added to 3.2

cheddar cheese whey at a concen ration of 40 gr m liters of potable water. Stage 2 was carried out in the per liter of potable water was heated at 121C. For 5 same manner as Stage 1. Stage 2 produced dry subminutes to produce a proteinaceous coagulum. The 00- stance yeast equivalent to 37% of the lactose supplied.

agulum was removed by filtration. The liquid fraction The Stage 2 yeast contained 7.03% N and'1.52% P. is called whey. Per liter of filtered whey solution the Preparation of Yeast Glycan following were added ammon um ulf g-; P The cells were harvested and washed by centrifugatassium phosphate, 5.0 g.; yeast extract powder, 1.0 g. tion. The cells contained in 750 m1. of slurry at 11.8%

The reaction was adjusted to pH 5.4 by the addition of solids were ruptured at 15C. by three passes through sulfuric acid. The broth was dispensed in Fernback a Manton-Gaulin homogenizer at 8-10.000 psig. The flasks fitted with baffles in 1 liter volumes and sterilized homogenate was adjusted to pH 9.5 with sodium hyin the autoclave. This primary Stage as in00ulated droxide, diluted to 5.9% solids and held for 30 minutes with 10 m1. of a glucose peptone yeast extract broth t 15C, Upon centrifugation of the homogenate, the culture of Saccharomycesfragilis Y-1l09. The primary i soluble solids were deposited in two layers. The stage was incubated for 3 days by revolving on a rotary upper layer constitutes the unrefined yeast glycan, the shaker at 112 RPM with a 4 inch eccentric throw at lower layer contains unruptured cells and some yeast 30C. glycan. The lower layer was resuspended in 200 ml.

Primary stage yeast equivalent to 5.0 g. dry substance 6 water and centrifuged to again form two layers. The was used to stock Stage 1 in a small fermentor. The upper layer was harvested and combined with the prestock yeast was added to 3.2 liters of potable water. lmvious upper layer. The combined upper layers were remctliatcly a liquid feed stock containing the following peatedly washed with 200 ml. portions of water. The

was supplied to the yeast in the l'crmentor. Feed stock results of the washing are presented in Table 111. The

washed yeast gum was lyophilized to a dry powder. The analysis of the dry powder is presented in Table IV. The rehydration-viscosity characteristics are presented in Table V.

EXAMPLE NO. 2

Preparation of Yeast Glycan from Candida utilis.

Preparation of Biomass:

The yeast Candida utilis Y-l084 was inoculated into 10 ml. of sterile glycose peptone yeast extract broth and incubated 2 days at 30C. This broth culture was used to inoculate 1 liter of sterile molasses broth of the following composition; clarified cane molasses reducing substance equivalent by Munson Walker gravimetric method, 30.0 g.; ammonium sulfate, 4.55 g.; diammonium phosphate, 0.68 g.; potassium sulfate, 0.20 g.; magnesium heptahydrate, 60 mg. The 1 liter of molasses broth was contained in a 4 liter Ehrlenmeyer flask. The reaction was adjusted to pH 5.2 by the addition of sulfuric acid before sterilization in the autoclave. This molasses broth growth stage was called the primary stage. After inoculation it was incubated for 3 days at 30C. on a rotary shaker revolving at l 1 2 RPM with a 4 inch eccentric throw.

Primary stage yeast growth equal to 5.0 g. dry substance yeast was used to stock a small fermentor containing 3.2 liters of potable water. This was called Stage 1. lmmediately, a liquid feed was supplied to the water suspension of yeast. The liquid feed comprised two solutions. Solution l contains 150 g. clarified cane molasses reducing substances equivalent by Munson Walker gravimetric method diluted to 1 liter with potable water. Solution 2 contained 29.9 ml. of 29% ammonia, 12.8 g. ammonium sulfate, and 2.58 ml. of 85% phosphoric acid in a volume of 1 liter potable water. The liquid feed was delivered continuously for 11 hours at an hourly increasing rate of 1.14. The temperature of the growth broth was 35C. Aeration was provided at a rate of 3 volumes air per volume of growth broth per minute using a sparger and impellor system. The reaction was maintained at pH 5.0-7.0.

Stage 1 produced yeast dry substance equivalent to 54.3 percent of the molasses provided. This Stage 1 yeast contained 8.69% N and 1.3% P.

Stage 1 yeast was used to stock Stage 2. Stage 2 liquid feed comprised two solutions. Solution 1 contained 150 g. clarified cane molasses reducing substances equivalent by Munson Walker gravimetric method. Solution 2 contained 33.3 ml. 29% ammonia, 17.3 g. ammonium sulfate, and 3.34 ml. of 85% phosphoric acid. Stage 2 was stocked with 16.4 g. d.s. of Stage 1 yeast by adding the Stage yeast to 3.2 liters of potable water contained in a small fermentor. The liquid feed was delivered immediately and continuously for 11 hours at an hourly increasing rate of 1.14. The reaction of the growth broth was between 5.5 and 6.8. The growth broth temperature was 35C. Aeration was provided at a rate of 3 volumes of air per volume of growth broth using a sparger and impellor system.

Stage 2 produced yeast dry substance equivalent to 45% ofthe weightof the clarified cane molasses reducing substance supplied. The Stage 2 yeast contained 8.03% N and 1.12% P.

EXAMPLE NO. 3

Preparation of Yeast Glycan from Saccharomyces carlsbergensis.

Saccharomyces carlsbergerisis (brewers yeast) was obtained as a by-product of the brewing operation at the St. Louis, Miss. plant of Anheuse'r-Busch, Incorporated. The cells were washed three times with water.

The cells contained in 400 ml. of slurry at 4.3 solids were ruptured at 15C. by three passes through a Manton-Gaulin homogenizer at 8000 psig. The homogenate was adjusted to pH 9.5 with sodium hydroxide, and held for 30 minutes at 15C. Upon centrifugation of the homogenate, the insoluble solids were deposited in two layers. The upper layer, which constitutes the unrefined yeast glycan, was harvested, and the lower layer, which contains unruptured cells and some yeast glycan, was resuspended in 200 ml. of water and centrifuged to again form two layers. The upper layer was harvested and combined with the previous upper layer. The combined upper layers were repeatedly washed with 200 ml. portions of water. The results of the washing as presented in Table III. The washed yeast gum or glycan was lyophilized to a dry powder. The analysis of the dry powder is presented in Table IV. The rehydration viscosity characteristics are presented in Table V.

EXAMPLE NO. 4

Preparation of Yeast Glycan from Candida utilis 1,300 grams each of Candida utilis Y-900 and Y- 1084, pH 6, at 7.5 and 6.0% solids respectively were ruptured at 15C. by three successive passes through a Manton-Gaulin homogenizer at 8,000 psig. The homogenates were adjusted to pH 9.5 with sodium hydroxide and held for 30 minutes at 15C. Upon centrifugation of the homogenate, the insoluble solids were deposited in two layers. The upper layer constitutes the unrefined yeast glycan, the lower layer contains unruptured cells and some yeast glycan. The lower layer was resuspended in 200 ml. water and centrifuged to again form two layers. The upper layer was harvested and combined with the previous upper layer.- The combined upper layers were repeatedly washed with-200 ml. portions of water. The results of the washing are presented in Table 111. The washed yeast glycan was lyophilized to a dry powder. The analysis of the dry powder is presented in Table IV. The rehydration-viscosity characteristics are presented in Table V.

EXAMPLE NO. 5

Preparation of Yeast Glycan From Saccharomyces cerevisiae.

Bakers yeast (Saccharamyces cerevisiae) was. grown in aerated batch culture on a combination of beet and cane molasses using suitable nutrients and nitrogen sources in accordance with Example No. 2 except that Saccharomyces cerevisiae was used. Final yeast concentration was '30 grams per liter dry solids yeast. The yeast was separated from the beer by centrifugation and was subsequently given three water washes and thickened to 11% solids by weight.

Fifty gallons of this suspension containing 46 pounds of yeast solids were cooled to 45F., subjected to homogenization at a pressure of 8,000 P516, and cooled to 45F. The homogenization procedure was repeated for a total of three passes. The homogenate was diluted to a volume of gallons with water. A food grade alkaline reagent (sodium hydroxide) was added until a pH of 9.5 was reached. The material was agitated for 15 minutes, and then centrifuged. The alkali extract, which contained 31 pounds of dry solids, was discarded. The centrifuge sludge, which contained l6 pounds of .dry solids, was diluted to 90 gallons with water and additional sodium hydroxide was added until a pH of 9.5 was reached. The slurry was agitated for 15 minutes, and then centrifuged. The alkali washings which contained pounds of dry solids, was discarded. The centrifuge sludge contained 1 1 pounds of dry solid which was comprised essentially of whole yeast cells and cell wall fragments. The washed sludge was diluted to 34 gallons with water. A food grade acid reagent, hydrochloric acid, was added until a pH of 6.5 was reached. The suspension was separated on a disc centrifuge operated in a flooded condition to yield 6 pounds (dab) of an underflow of which consists principally of whole cells and a minor amount of cell wall fragments, and 5 pounds (dsb) overflow which consists principally of cell wall fragments and a very minor amount of whole cells. The overflow was vacuum concentrated on a plate evaporator and flask dried in a spray dryer to 7.9 percent moisture. Product analysis was as follows:

of the rehydrated glycan andthe effect of rehydration pH are shown in Table VI.

EXAMPLE N0. 5A

Preparation of Yeast Glycan from Saccharomyces cerevisiae Commercial bakers yeast was processed according to Example No. 5 to obtain the centrifuge sludge and alkali extract. The centrifuge sludge is further processed by homogenization and washing. The centrifuge sludge (15 gallons) was diluted with an equal volume of water, and cooled to 45F., and homogenized at 8,000 P816 in a Manton-Gaulin homogenizer. The homogenate was recycled with intermediate cooling to 45F. for a total of three passes. The homogenate was diluted to gallons with water, adjusted to pH 9.5 by the addition of sodium hydroxide and centrifuged to a supernate and a residue. This residue was suspended to a total of 45 gallons and centrifuged to constitute one wash. The residue was washed again. The twice washed residue was adjusted to pH 5.3 by the additionof hydrochloric acid and spray dried.

The composition of the spray dried glycan was (dsb): 92.5% carbohydrate, 6.3% crude protein, 2.0% nucleic acid, 0.9% ash, and 0.3% lipid.

TABLE VI The Effect of a Process Variable Upon the Viscosity of Rehydrated Glycan Example No. 5 shows the large scale preparation of yeast glycan. At a point in the preparation, the centrifuged sludge is diluted, adjusted to pH 9.5, agitated for fifteen minutes, and then centrifuged. if the fifteen minute time period is prolonged, then the spray dried glycan subsequently obtained has a markedly increased viscosity after rehydration. The spray dried glycans were made to a I07: W/W suspension at 25C., and rapidly adjusted to pH 3. 5. 7 and 9. The viscosity was measured with time.

Process Maximum Viscosity (cps) ofa 10% W/W Suspension Holding Time Measured at 25C.. at the noted rehydration pH.

Sample F, pH 9.5 pH 3 pH 5 pH 7 pH 9 091127 A 36 hours 31,800 41,800 50,500 37.800- 09:127 B 30 hours 23,000 33,800 34,500 24,700 09:127 C 3 hours 8,800 13,800 12,300 10.400

Carbohydrate. dsb The hold time may be at pH- about 9.5 to about 10.0, 71 Crude protein, dsb 15.0 f bl b H 9 f b 3 b 30 h I nucleic acid dsb 28 pre era y a out p .5, or a out to a out ours, 71 Lipid. dsb 0.8 at a temperature of from about 40F. to about 122F. dsb If the hold time is used in the process involving The viscosity of the rehydrated glycan is a function of several variables. Examples of these variables are l) rehomogenization of the yeast glycan cell wall debris, it occurs after homogenization and before washing or method or processing to obtain the dried glycan, (2) drying.

dehydration time, (3) rehydration temperature, (4) rehydration pH, and (5) the concentration of the glycan. The effect of processing technique upon the viscosity Glycan preparations from the various strains of yeast may or may not show an effect of pH upon viscosity as noted in Table Vll.

TABLE VII The Effect of pH on the Viscosity of Yeast Glycan Preparations Yeast glycan was prepared from various strains of yeast in accordance with the procedures described in the Examples except that the samples were not subjected to freeze drying or spray drying. These yeasts glycan sludges were adjusted to H 3. 5. 7 and 9. carefully diluted to 1071 NW solids. and incubated at 25C.

viscosity was measured periodically over a four hour period to obtain the maxnnum viscosity using a Brookfield LVT. Helipath Stand, Spindle TE at 12 The temperature of rehydration markedly affects the viscosity of a glycan preparation as noted in Table Vlll.

TABLE VH1 ken yeast cells were decreased by rehomogenization passes, which in turn allows yeasty flavor to be totally Effect of Rehydration Concentration & Temperature Upon Viscosity transferre to a 25C. bath. When the 95C. had reached 25C., its viscosity and the viscosity of the initial 25C. sample were measured at 25C. using a Brookfield LVT,

Helipath Stand. Spindle 'lTE at 12 rpm.

Viscosity (cps) Rehydration Rehydration Temperature 25C. 95-100C. for 5 min. pH

Sample No. 09:125

at 5% W/W 200 415 at 10% W/W 1330 13,300 6.5 at W/W 84000 84000 Sample No. 09:127C

at 5% 166 580 at 10% 9150 10800 6.2 at 20% 84000 84000 Sample No. 09:127B

at 2.5% 166 380 at 5.0% 166 2900 6.0 at 10.0% 21600 84000 Sample No. 09:127A

at 2.5% 166 540 at 5.0% 166 5800 5.8 at 10.0% 38000 84000 Sample No. 091126 at 5.0% 330 330 at 10.0% 3870 3860 6.0 at 20.0% 84000 86000 Effect of Glycan Purity Upon Flavor and Functionality Fifty gallons of a suspension of commercial bakers yeast at 12% solids, F. was passed three times through a Manton-Gaulin homogenizer at 8000 PSIG with cooling at F. The homogenate was diluted to 125 gal.. adjusted to pH 9.5 with sodium hydroxide, agitated for fifteen minutes, and centrifuged to yield a cell wall sludge and an alkali extract. The cell wall sludgewas diluted with an equal volume of water. cooled to 45F.. subjected to 0. 1. 2 and 3 passes through a Manton-Gaulin homogenizer at 8000 F810. 45F.. diluted with an equal volume of water. adjusted to pH 9.5 with sodium hydroxide, and centrifuged to give a rehomogenized cell wall sludge. The "rehomogenized" cell wall sludge was diluted with three volumes of water and centrifuged to give a once washed yeast glycan sludge. The washing process was repeated to give a twice washed yeast glycan sludge which was'then adjusted to pH 5.2-5.5 with hydrochloric acid. Samples of the yeast glycan were removed for solids and viscosity measurements. The remainder of the glycan sluge was spray dried. The spray dried glycan w ts analyz e d for crude protein content TK eldahl NX625), flavor, and viscosity. V 7

Not Not Yeasty Yeasty The data of Table lX shows that the extent of purification affects the functionality and flavor ofthe glycan. Purification of the glycan was indicated by the decrease in the content ofcrudc protein and of unt'ractured yeast cells. This probably means that the content of unbroremoved by washing.

Another beneficial effect was an increase in viscosity as the number of rehomogenization passes was increased. It is not clear if the increase in viscosity was due to a possible decrease in whole cell content, to a decreased content of protein, or simply to a possible decrease in particle size.

The equation representing the relationship between whole cells and crude proteins is:

% whole cells 2X(% crude protein) 10 5.0% crude protein. Furthermore, extrapolation to.

100% whole cells shows that the crude protein content of whole cells is 55%, which is in agreement with the value found for whole cells.

The data of Table IX shows that when the protein level is above about the flavor of the glycan suffers. Thus, the protein content is from about 5 to 20% and the content of whole cells is 0 to about 30%. With other method of cell rupture purification and drying, the protein content may fall within the foregoing range even though the whole cell content is at a very low level.

Comparison of the viscosities of the glycan sludge to that of the spray dried glycan reconstituted to the same solids content in Table IX shows that the act of spray drying can increase the viscosity.

If the glycan is freeze-dried instead of spray dried, the viscosity when reconstituted is reduced.

TABLE X Comparison of the Viscosities of Freeze Dried and Spray Dried Glycan Part of the glycan leed of Isolation No. 128 was freeze-dried and part spray dried. The freeze-dried and the spray dried powders were reconstituted to 10% W/W suspensions. The viscosity of the suspensions was measured at C. after tempering for 0, I, 2, 4, 24 hours at 25C.

Spray dried F reeze-dried Viscosity (cps) 0 hrs. 5000 0 1 6600 0 2 7700 0 4 8100 I000 24 9200 8500 The viscosity of freeze-dried glycan increases on long standing in aqueous suspension.

To be certain that the starting whole cells do not affect viscosity of aqueous systems, we have measured the viscosities of mixtures of spray dried glycan and spray dried whole cells. The results are shown in Table XI. The results are given in centipoises. The viscosity is measured at 25C.

The whole cells are spray dried unfractured bakers yeast. The yeast glycan is from bakers yeast and contains about 9.1% crude protein.

In addition to the aforementioned viscosity characteristics, suspensions of yeast glycan have additional important attributes such as a bland flavor, a "fat-like mouth feel, and a sheen or gloss in appearance. By a fat-like mouth feel is meant that a material will impart a thick, oily sensation without a gummy or sticky sensation.

Furthermore, yeast glycan can serve as a source of energy. The bioavailability of the energy of a yeast glycan was measured at WARF Institute, Inc. according to a slightly modified procedure of E.E. Rice, Journ. of Nutrition, 61 (1957). The value of 3.52 calories per gram was obtained for a bakers yeast glycan made in accordance with Example No. 5. The Parr bomb calorimeter technique measured 3.70 calories per gram. The composition of the glycan was 7.9% moisture, 11.6% protein, 2.7% nucleic acid, 1.1% lipid, 7.0% ash, 9.9% crude fiber, and 59.1% carbohydrates. The biocaloric content of this yeast glycan is 3.83 calories per gram (dsb) as compared to sucrose at 3.85 calories per gram. The caloric content of the yeast glycan is about that of starch and protein, which is less than one-half that of fats and oils.

At the present time, at least 10 percent oil is required in even low-calorie products suchas low calorie spoonable salad dressings, in order to obtain the fat-like mouth feel. We have found that the oil content of many food systems can be further reduced if yeast glycan is incorporated. Formulation ofsome of these systems are presented in Examples 6, 7, 8 and 9. The counterpart system is also presented.

EXAMPLE NO. 6

Chocolate Thick Shake gram.

Separately blend the dry and wet ingredients. Add the dry mix to the wet, increasing the mixer speed as necessary. Mix for three minutes. Chill or freeze.

EXAMPLE NO. 7

Chocolate Instant Pudding Yeast Glycan Formula Counterpart Ingredient 7c \V/W Liquid Skim Milk 73 A commercial preparation containing: water, sugar,

Granulated Sugar 14 NFMS, whey solids with -Continued Chocolate instant Pudding -Continued Sour Cream Type Dip Yeast Glycan Formula Counterpart yeast Glycan Formula Counterpart Ingredient 7b W/W calcium hydroxide and disodium Ingredient 7c W/W Yeast y l P P modified tapioca Yeast Glycan 9.0 is made with sour cream to i i hydrogenated Vegetable which onion and flavorings Breakfast Cocoa 2 Oil. cocoa processed with Rogers Toasted are added alkali. sodium stearoyl -2- Onion 0' 5 Vanilla l lactylate. polysorbate 60. A ypicai recipe sorbitan monostearate. sodium Monosodium 4 case a sal dext ose. Glutamate 0.2 Sour cream v2 pint Calories 93/100 carrageenan. guar gurn. Basic grams artificial color and flavor. V table Onion and 150 calories/100 gram. Fresh Flavor" Flavorings Y4 ounces Procedure: Onion Separately blend the dry and wet A Calories 180/ I00 grams ingredients. Add the dry mix to g the wet and continue to mix at medium Ono y rate 02 speed until the pudding begins to thicken. Chill for serving. Calm 66/ grams Procedure:

Using an electric mixer. blend the The flavor, mouthfeel, texture and appearance of the g x g 2 Li butiermllkchocolate instant pudding formulated with yeast glycan l gamls c was directly comparable to the commercial product.

EXAMPLE NO. 8 The flavor, mouthfeel, texture, and appearance of the sour cream type dip formulated with yeast glycan was directly comparable to the commercial product.

Thousand island Salad Dressing EXAMPLE NO. 10

Yeast Glycan Formula Counterpart Ingredients 7( W/W Water 52.4 A commercial low calorie lmltanon Mayonnaise (low calorie) preparation containing: water. Chili Sauce 20.0 vinegar. soybean oil, sugar. Ingredients w/w counterpart tomato paste. pickle. egg yolk. Pickle Relish 10.0 salt. lemon juice. onion.

gum "agacamh flavoring Vinegar 6.0 commercial low calorie Vegetable Oil 6.8 red peppers, propylene I limitatio mayonnaise l l, l i Spices Lemon uice 2.0 containing: water. vegetable Yeast Glycan 5.4 artificial color. calcium o l; starch. vinegar. salt.

disodium EDTA. [68 Salt 1.5 egg yolks. saccharin. E g yolk 2.0 calories/100 grams. sodium benzoate. EDTA. \fhite vinegar 4O Mustard 0.25 flavorings and color. (5 grain) 2.0 Onion 0.025 Sucrose 1.4 Garlic 0.025 Saccharin 0.020 Calories l26/l00 Water 68.68

grams B.

Vegetable oil 10.0v Procedure for Yeast Glyca n Formula: E yolk -4 0 136 calori s/[O0 grams 1. Place the water and Oll in a Yeast glycan 7.5

blender. Set the blender at the Cal ri s 102/100 lowest speed. Add the yeast glycan. grams After the yeast glycan IS dispersed p d gradually increase the blender Speed 1. Place ingredients in Part A in a blender. Set blender at until the yeast glycan oil and water 1 Speed. Mix 0 a a w n e l 'F f 2. Add oil and egg yolk and mix well at high speed. Add P mush l and 3. Set blender at high speed and mix in yeast glycan. egg x y s bahc- Blend 4. Continue mixing at high speed, until contents well. Chill tor serving. Se [0 a Soft gd 5. Homogenizc mixture for further smoothness.

The flavor, mouthfeel. texture and appearance of the 4 Thousand Island Salad Dressing formulated with yeast What is claimed is: glycan was directly comparable to the commercial 1, A yeast product comprising yeast fragments and product. whole cells containing on a dry solids basis from about 5 to about 20% crude rotein, from about 0.1 to about EXAMPLE NO. 9 P

3 percent nucleic acid, from about 0.1 to about 3 percent lipid, from about 0.5 to about 3 percent ash, and Sour Cream Type Dip from about 60 to about 95 percent carbohydrate, and C having a minimum viscosity of 500 centipoise when Glyca Fmmul oumerpan suspended in a 10 percent aqueous suspension, said I product having a majority of irregular cell wall fragllilgiedlem w/w ments and having a minor amount of whole cells.

i uid Bljlmrmim 900 A conventional Sour cream 2. A product according to claim 1 having greater dip (cookbook recipe) than 3,500 centipoise in said 10 percent suspension.

3. A product according to claim 1 derived from Saccharomyces cerevisiae, Saccharomyces carlsbergensis, Saccharomyces fragilis, and Candida utilis.

4. A process for the production of yeast glycan comprising the steps of:

A. Growing a food grade yeast,

B. Harvesting and washing the yeast biomass,

C. Rupturing the yeast cells,

D. Extracting the ruptured yeast cells at a pH of 5.5

to 11 for up to about 60 minutes,

E. Separating the insoluble glycan from soluble cytoplasmic materials, and

F. Recovering a yeast glycan product having a major amount of irregular cell wall fragments and a minor amount of whole cells.

5. The process of claim 4 including the step of A. Washing the recovered glycan with water,

B. Concentrating the glycan, and

C. Drying the glycan to recover a product containing on a dry solids basis from 5 to 20% crude protein, from O.l to 3% nucleic acid, from 0.1 to 3% lipid, from 0.5 to 3% ash, and from 60 to 95% carbohydrate.

6. A process according to claim 5 wherein the viscosity of the glycan is increased by incubating at pH 9.5 prior to drying.

7. A process according to claim 5 wherein the glycan is spray dried.

8. A process according to claim 4 in which the yeast is selected from the group consisting of Saccharomyces cerevisiae, Saccharomyces carlsbergensis, Saccharomyces fragilis, and Candida utilis.

9. A process according to claim 4 wherein the yeast cells are ruptured by homogenization below about 10. A process according to claim 4 wherein the ruptured yeast cells are extracted as a pH between about 6 and about i l and a temperature between about 25 and about 60C. for about 5 to abaout 60 minutes.

11. A process according to claim 4 wherein the ruptured yeast cells are extracted at a pH of about 9.5 and a temperature between 25C. and 60C. for 5 to 60 minutes.

12. The process according to claim 4 wherein the insoluble glycan is separated by centrifugation.

13. A process according to claim 5 wherein the protein content of the glycan is reduced to a constant amount by repeated aqueous washings.

14. A process according to claim 4 wherein the protein content of the glycan is reduced by homogenization and aqueous washing prior to recovery of the glycan.

15. A process according to claim 4 including the steps of:

A. Homogenizing the separated glycan,

B. Washing the homogenized glycan with water, and

C. Drying the glycan to recover a product containing on a dry solids basis from 5 to 20% crude protein, from 0.1 to 3% nucleic acid, from 0.1 to 3% lipid, from 0.5 to 3% ash. and from 60 to carbohydrate.

16. The process of claim 4 including the step of rehydrating the separated insoluble glycan and holding the same for about 3 to about 30 hours at a pH of about 8.5 to about 10 and a temperature of about 40F. to about 122F. 

1. A yeast product comprising yeast fragments and whole cells containing on a dry solids basis from about 5 to about 20% crude protein, from about 0.1 to about 3 percent nucleic acid, from about 0.1 to about 3 percent lipid, from about 0.5 to about 3 percent ash, and from about 60 to about 95 percent carbohydrate, and having a minimum viscosity of 500 centipoise when suspended in a 10 percent aqueous suspension, said product having a majority of irregular cell wall fragments and having a minor amount of whole cells.
 2. A product according to claim 1 having greater than 3,500 centipoise in said 10 percent suspension.
 3. A product according to claim 1 derived from Saccharomyces cerevisiae, Saccharomyces carlsbergensis, Saccharomyces fragilis, and Candida utilis.
 4. A PROCESS FOR THE PRODUCTION OF YEAST GLYCAN COMPRISING A. GROWING A FOOD GRADE YEAST. B. HARVESTING AND WASHING THE YEAST BIOMASS, C. RUPTURING THE UEAST CELLS, D. EXTRACTING THE RAPTURED YEAST CELLS AT A PH OF 5.5 TO 11 FOR UP TO ABOUT 60 MINUTES, E. SEPARATING THE INSOLUBLE GLYCAN FROM SOLUBLE CYTOPLASMIC MATERIALS, AND F. RECOVERING A YEAST GYLCAN PRODUCT HAVING A MAJOR AMOUNT OF IRREGULAR CELL WALL FRAGMENTS AND A MINOR AMOUNT OF WHOLE CELLS.
 5. The process of claim 4 including the step of A. Washing the recovered glycan with water, B. Concentrating the glycan, and C. Drying the glycan to recover a product containing on a dry solids basis from 5 to 20% crude protein, from 0.1 to 3% nucleic acid, from 0.1 to 3% lipid, from 0.5 to 3% ash, and from 60 to 95% carbohydrate.
 6. A process according to claim 5 wherein the viscosity of the glycan is increased by incubating at pH 9.5 prior to drying.
 7. A process according to claim 5 wherein the glycan is spray dried.
 8. A process according to claim 4 in which the yeast is selected from the group consisting of Saccharomyces cerevisiae, Saccharomyces carlsbergensis, Saccharomyces fragilis, and Candida utilis.
 9. A process according to claim 4 wherein the yeast cells are ruptured by homogenization below about 50*C.
 10. A process according to claim 4 wherein the ruptured yeast cells are extracted as a pH between about 6 and about 11 and a temperature between about 25* and about 60*C. for about 5 to abaout 60 minutes.
 11. A process according to claim 4 wherein the ruptured yeast cells are extracted at a pH of about 9.5 and a temperature between 25*C. and 60*C. for 5 to 60 minutes.
 12. The process according to claim 4 wherein the insoluble glycan is separated by centrifugation.
 13. A process according to claim 5 wherein the protein content of the glycan is reduced to a constant amount by repeated aqueous washings.
 14. A process according to claim 4 wherein the protein content of the glycan is reduced by homogenization and aqueous washing prior to recovery of the glycan.
 15. A process according to claim 4 including the steps of: A. Homogenizing the separated glycan, B. Washing the homogenized glycan with water, and C. Drying the glycan to recover a product containing on a dry solids basis from 5 to 20% crude protein, from 0.1 to 3% nucleic acid, from 0.1 to 3% lipid, from 0.5 to 3% ash, and from 60 to 95% carbohydrate.
 16. The process of claim 4 including the step of rehydrating the separated insoluble glycan and holding the same for about 3 to about 30 hours at a pH of about 8.5 to about 10 and a temperature of about 40*F. to about 122*F. 